The present invention relates to a transmitter module, receiver module, or transmitter and receiver module in optical communication. Especially it relates to a surface mounted type optical communication device that can achieve the reduction of substrate cost.
As a transmitter module in an optical communication device, three-dimensional semiconductor laser module 1 as shown in FIG. 1 has been successfully manufactured and marketed. A transmission signal is converted into light by semiconductor laser 2, and transmitted to optical fiber 13 via lens 9 and ferrule 12. On base 4 which is called a header, photodiode 3, semiconductor laser 2 and attaching pole 5 are housed within cap 7, and the entirety is housed inside lens holder 10. This module is electrically connected to the outside of housing 11 by lead pins 6.
Recently, another type of transmitter and receiver module has been proposed, in which a wavelength division multiplexing filter (hereinafter referred to as a WDM filter in the present specification and claims), a photodiode (hereinafter referred to as a PD in the present specification and claims), and a semiconductor laser (hereinafter referred to as an LD in the present specification and claims) are installed ({circle around (1)} p208, xe2x80x9cReceptacle Type Bidirectional Wavelength Division Multiplexing Optical Modulexe2x80x9d written by Masahiro Kogusu, Tazuko Tomioka, and Shigeru Oshima, Electronics Society 1996 of the Institute of Electronics, Information and Communication Engineers, C-208). (There are PD/LD descriptions in the embodiments of the present specification and claims; however, this means either a PD or an LD, or an optoelectronic converter device equivalent to these).
However, the three-dimensional module needs many parts including the housing and it consumes time to align the optical axes, so its material cost and manufacturing cost are currently high. In order to reduce the cost and size of the three-dimensional module, a surface mounting type module 14 as shown in FIG. 2 is being developed (Japanese Unexamined Patent Publication No. 332989 of 1998).
In this module, the package surface and the optical fiber surface are parallel to each other, and light is propagated horizontally near the substrate surface. The space between the end of the optical fiber and the LD/PD can be reduced to be extremely narrow. Therefore, this module is small in size, and when the module is mounted on a printed circuit board, the optical fiber is in parallel with the printed circuit board, so that the circuit board does not greatly increase in size. Therefore, it can be expected that the parts cost is reduced and alignment becomes unnecessary. An Si semiconductor single crystal substrate (hereinafter referred to as an Si bench in the present specification and claims) 16 is provided inside mount 15 which is a package of the module 14. Optical part LD/PD 19 and optical fiber 22 are attached to the Si bench 16.
Large V groove 17 and V groove 18 are formed at the center part of the Si bench 16 by means of anisotropic etching. LD/PD 19 is attached to upper step portion 20 which is one step higher than the portion with the V groove. A metallized pattern is printed on this upper step portion. The LD/PD 19 is fixed at a predetermined position based on an alignment mark. Ferrule 21 is pushed against the large V groove 17, and optical fiber ribbon 22 at the front end of the ferrule is pushed against and fixed in the V groove 18. The advanced development of photolithography technology enables accurate positioning of the optical fiber and optical parts. The use of the Si semiconductor single crystal as a bench has such advantages.
In the surface mounting type module, highly accurate photoetching technology for the semiconductor technology enables to form accurately the large V groove 17 and the V groove 18 which fix the optical fiber onto the Si bench, the metallized pattern for fixing the LD/PD 19, and the alignment mark. Since the optical fiber is positioned by the large and small V grooves and the optical parts are mounted at correct positions based on the mark, the optical parts are caused to exist correctly on the optical axial line of the optical fiber. Even if the LD is not caused to emit light for alignment, the fiber can be mounted. Hence this method is called passive alignment. By this technology, mounting can be automatized, and the cost reduced. More specifically, the material cost and assembly cost are reduced to be lower than those of the module of FIG. 1. Therefore, it is considered that a small-sized transmitter/receiver of a low price can be achieved by this surface mounting. However, the material cost for the Si bench increases the price of the module. The Si bench requiring Si with a wide area is high cost part which influences the total cost of the module.
In actuality, among the devices comprising the surface mounting type transmitter and receiver module, including the LD, PD, package (resin package), lead frame, and Si bench, the most expensive part is the Si bench. A reduction in the cost of the Si bench is essential to further lower the price of a transmitter module, a receiver module, and a transmitter and receiver module. A first object of the invention is to reduce the cost of the Si bench. A second object of the invention is to provide an inexpensive optical communication device by reducing the Si bench cost.
The present inventor, considering these points from various perspectives, noted that the accuracy in xcexcm units was required only at the optical coupling portion including the optical fiber front end and LD chip light emitting portion in the surface mounting device which is encircled by the broken line in FIG. 2 and FIG. 3. If this portion deviates, light from the LD cannot enter the optical fiber. Therefore, it is important that the optical coupling portion be in alignment. Strict accuracy is not required at other portions. Slight shifting of the ferrule causes no serious problem.
In the present invention, only the optical coupling portion which needs high accuracy is placed on the Si bench, and other devices and the Si bench itself are placed on another inexpensive retaining substrate. The cost per unit area of the retaining substrate is lower than the cost per unit area of the Si bench, so that the substrate cost can be reduced.
In the present invention, the Si bench is used only for the optical coupling portion. For the other portion a composite substrate structure formed from materials other than the Si semiconductor single crystal, for example, ceramic and a resin is used. The optical coupling portion is placed on the Si bench since it requires high accuracy. The other portion is placed on a retaining substrate that is lower cost and also lower accuracy. The Si bench and the retaining substrate are combined and used to meet the requirements of cost and accuracy. This is the core of the invention.
The optical communication device of the invention is comprised of an optical fiber, optical parts, and a substrate for optical coupling. The coupling portion between the optical fiber end part and the optical parts is fixed by a semiconductor substrate having V grooves formed by means of etching. And one portion at the other end of the optical fiber is fixed by a retaining substrate which is different from the abovementioned semiconductor substrate.